The 2018 AMG GT with its hand-built M178 4.0L twin-turbo V8 is a serious performance machine, but early examples suffer from catastrophic engine failures tied to bearing and piston issues. When it runs right, it's spectacular; when it doesn't, you're looking at five-figure engine work.
Connecting Rod and Main Bearing Failures
Occasional · high severityTypical onset: 30,000-60,000 mi
Symptoms: Sudden metallic knocking from engine bay, especially cold starts, Drop in oil pressure or oil pressure warning light, Metal shavings or glitter visible in oil during changes, Engine runs rough or misfires before catastrophic failure
Fix: Complete engine teardown to replace rod bearings and/or main bearings. If caught early, bearing replacement runs 20-30 hours. If spun bearing damaged crank or block, you're into short block or complete engine replacement at 40-60 hours. Mercedes extended warranty coverage on some VINs, but not all.
Estimated cost: $8,000-25,000
Piston Ring Land Failure and Piston Cracking
Occasional · high severityTypical onset: 40,000-80,000 mi
Symptoms: Excessive oil consumption, burning through a quart every 500-1,000 miles, Blue smoke from exhaust on startup or during hard acceleration, Misfires and rough idle as rings fail to seal, Loss of compression on one or more cylinders
Fix: Requires engine removal and complete tear-down. Replace all pistons and rings, inspect cylinder walls for scoring. Often combined with bearing work since engine is already out. Labor runs 35-50 hours for piston replacement with head removal. Some techs recommend just doing a factory short block at this point.
Estimated cost: $12,000-22,000
Transmission Oil Cooler Leaks
Common · medium severityTypical onset: 50,000-90,000 mi
Symptoms: Transmission fluid puddles under car, usually passenger side, Burning smell after spirited driving, Transmission temperature warnings on dash, Fluid visible on undertray during inspection
Fix: Replace transmission oil cooler and lines. Requires dropping undertray and partial exhaust work for access. Cooler itself isn't expensive, but labor for proper installation and fluid refill with correct MB spec fluid runs 4-6 hours. Flush system if contamination suspected.
Estimated cost: $1,200-2,200
Transmission Mount Failures
Common · medium severityTypical onset: 40,000-70,000 mi
Symptoms: Clunking when shifting from Park to Drive or Reverse, Vibration through chassis during acceleration, Excessive driveline movement visible during hard launches, Thud felt through floorboard on deceleration
Fix: Replace rear transmission mount. Common wear item on high-torque applications. Access requires lift and removing heat shields. Mount itself is pricey from Mercedes. Budget 3-4 hours for replacement. Inspect driveshaft carrier bearing and guibo while you're under there.
Estimated cost: $800-1,400
Driveshaft Coupling (Guibo) and Center Support Bearing Wear
Occasional · medium severityTypical onset: 60,000-100,000 mi
Symptoms: Vibration at highway speeds, especially 65-80 mph, Clunking during hard acceleration or deceleration, Squeaking or squealing from under car during takeoff, Visible cracking in rubber flex disc during inspection
Fix: Replace flex disc (guibo) and center support bearing. Related to NHTSA recall for driveshaft on some VINs—check if yours was covered. Even if recall was done, these wear over time with hard use. Driveshaft removal required, 4-5 hours labor. Use OE Mercedes parts; aftermarket flex discs fail prematurely on this torque level.
Estimated cost: $1,200-2,000
Fuel Filter Clogging and Fuel System Contamination
Occasional · medium severitySymptoms: Hesitation or stumble during hard acceleration, Intermittent limp mode with reduced power warnings, Hard starting after sitting, especially in heat, Fuel trims way off during diagnostics
Fix: Replace in-tank fuel filter assembly and pump module if contaminated. Mercedes originally spec'd lifetime filter, but that's optimistic with modern ethanol fuel. Access through rear seat area, 3-4 hours. If contamination is severe, may need fuel system flush and injector cleaning. Some cars got bad fuel from factory storage—check service bulletins.
Estimated cost: $900-1,800
Software Glitches in Infotainment and Driver Assistance
Common · low severitySymptoms: COMAND system freezes or reboots randomly, Backup camera black screen or delayed display, Bluetooth connectivity drops repeatedly, Navigation system crashes or loses route
Fix: Multiple NHTSA recalls for software updates. Dealer must flash latest firmware—cannot be done aftermarket in most cases. Takes 1-2 hours at dealer. Some issues persist even after updates due to hardware limitations in early MY2018 COMAND units. No parts cost if under recall, just programming time.
Estimated cost: $0-350
Buy only with comprehensive pre-purchase inspection including borescope and oil analysis, full service records, and budget for engine replacement—when they're good they're incredible, but the engine grenades are real and expensive.
AI-assisted summary drawn from NHTSA recall data, our labor-times database, and platform knowledge. Not a substitute for a pre-purchase inspection on a specific vehicle.